improve rendering performance even more by using instanced rendering

instancing_vertex.glsl

@@ -0,0 +1,13 @@
+#version 330
+
+in vec3 vertexPosition;
+in vec2 vertexTexCoord;
+in vec3 vertexNormal;
+in vec4 vertexColor;
+in mat4 instanceTransform;
+
+uniform mat4 mvp;
+
+void main() {
+    gl_Position = mvp * instanceTransform * vec4(vertexPosition, 1.0);
+}